1. Field of the Invention
The present invention relates to a novel suspended membrane structure, suitably usable in constructions with a relatively large span.
2. Description of the Prior Art
The membrane structures presently used in general take the form of an air-supported membrane structure, a suspended membrane structure or a membrane-sheeted frame structure.
The air-supported structure comprises a membrane made to outward swell with a relatively small curvature, in other words, made to have a curved surface with a so-called small rise or arch, where the wind pressure applied to the membrane is allowed to act as a negative pressure as far as possible, so that a well-balanced resistance to wind can be exhibited.
Also, reinforcing cables may be appropriately provided to the membrane, so that it becomes possible to keep a huge span as exemplified by an indoor base ball field.
However, air must be always supplied to maintain the shape of the membrane surface, accompanying a very troublesome management for the maintenance, requiring a considerable expense, and bringing about the problem that this structure is unsuitable from an economical viewpoint when used in constructions of a medium or small span of 100 m or less.
Moreover, because of its inside necessarily constructed to prevent escape of air and to define a closed space, the comfortableness due to the openness or air-freshness can not be expected, also lacking in a sense of the seasons.
Referring to the suspended membrane structure, this has the advantages that the membrane is expected to have a membrane stress resistance inherent in the membrane structure itself, can be readily applied with prestress, and can give a beautiful form, and also has the feature that a large-scale continuous space can be obtained when the suspended membrane structure is of a post type.
However, when the suspended membrane structure of a post type is employed, the post can be an obstruction depending on the use of the structure. Also when it is of a single arch type, there is the problem that an unbalanced tensile force distribution at both sides of the arch may make poor the balance of the arch and make it difficult for a bearing frame to be well self-supported.
FIG. 18 illustrates an example of the above membrane-sheeted frame structure, in which a membrane 3 is spread on the top of a self-supporting frame 1 with a secondary member 2 held therebetween.
This membrane-sheeted frame structure has the features that the frame can be well self-supported and can form a freely curved surface. It also has the advantage that there is no limitation to its plane or sectional configuration, and the structure can be designed with ease.
However, in the instance where the surface formed by the membrane 3 is spread on the grille of the space trussed frame 1 as in the example shown in FIG. 18, the point support system that utilizes the point of a top chord can promise with difficulty a sufficient strength, since the wind pressure applied to the membrane surface is transferred to the frame 1 through the point-supported portions.
Also, in an instance where a system is taken in which the membrane is successively supported along the frame 1, the above secondary member 2 is required in an excessive number so that the membrane surface can keep its shape, thus making it difficult to economically provide frame members.
In addition, the membrane 3 necessarily comes to have an excessively small size and curvature for a structural membrane, and hence can only have the function as a light-transmissive finishing member that covers the top of the frame 1, thus bringing about the problem that the system of the tensile force resistance by virtue of the membrane surface, which should be inherently possessed by the membrane structure, can not be said to have been sufficiently achieved.
Moreover, because of the frame 1 held beneath the membrane 3, only the form of the frame 1 may be emphasized to the persons inside the structure, resulting in a weakening of the beautifulness such as the lightness or comfortableness to be demonstrated by the curved surface of the membrane.